GATE CSE 1997 | Question: 6.10, ISRO2016-54

Question

Let $R (a, b, c)$ and $S(d, e, f)$ be two relations in which $d$ is the foreign key of $S$ that refers to the primary key of $R$. Consider the following four operations $R$ and $S$

1. Insert into $R$

2. Insert into $S$

3. Delete from $R$

4. Delete from $S$

Which of the following can cause violation of the referential integrity constraint above?

• A. Both I and IV

• B. Both II and III

• C. All of these

• D. None of these

Comments

UGC NET:

https://gateoverflow.in/225817/ugc-net-cse-july-2018-part-2-question-69 

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@Deepak Poonia sir in ugc question they gave options with will shouldn't it be can or may be there right ?

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Refer This For Future!!!

Operation	Target Table	Can cause violation?	Reason
Insert	$R$ (Parent)	No	Adding a parent row creates no orphans.
Insert	$S$ (Child)	YES	The new FK value $d$ might not exist in $R.a$.
Delete	$R$ (Parent)	YES	Deleting $a$ leaves child rows in $S$ referencing a missing row.
Delete	$S$ (Child)	No	Removing a child row leaves all parent rows intact.
Update	$R$ (Parent PK)	YES	Modifying $a$ breaks references from existing rows in $S$.
Update	$S$ (Child FK)	YES	Changing $d$ to a non-existent $a$ breaks the link.

 

Answer 1

$$\overset{R}{\begin{array}{|c|c|c|} \hline \textbf {a (PK)} &  \textbf {b} & \textbf {c} \\\hline  \text{1} \\\hline \text{2}  \\\hline \end{array}} \qquad \overset{S}{\begin{array}{|c|c|c|} \hline \textbf {d (FK referring to PK of R)} &  \textbf {e} & \textbf{f} \\\hline  \text{2} \\\hline \text{1}  \\\hline \end{array}}$$

• Insert into $R$ cannot cause any violation.
• Insert into $S$ can cause violation if any value is inserted into d of S, which value is not in a of R.
• Delete from $S$ cannot cause any violation.
• Delete from $R$ can cause violation if any tuple is deleted, and as a result a value in 'a' gets deleted which is referenced to by 'd' in $S.$

Correct Answer: $B$

Comments

This question build my referential integrity constraint concept very well

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Hey Aplogies if my thinking is too naive to think of given options in this way

The questions says Insert into R, then second option says Insert into S, which is fine right, now 3rd options reads, Delete from R and then 4the options Delete from S, which also seems fine if followed in order as i did, but if followed individually, options B and C, can cause violation, so

My question is how do i decided which appraoch to consider when solving/ underdstanding options like this as the question didnt mention to consider them as a group or an indvidual.

My sincere aplogioes again, im this is too naive.

Answer 2

2-Insert into S   and  3-Delete from R  ,can cause Violation of the Referential integrity constraints.

Hence ,ans  is  (B) Both II and III

Answer 3

Option (B) Both (II) and (III) Voilates the refential integrity constraints!!!

Answer 4

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